1. Field of the Invention
The present invention relates to a method of producing an electronic circuit and to an electronic circuit substrate.
2. Description of the Related Art
Conventionally, when producing an electronic circuit substrate, a conductor pattern is formed by performing resist coating on a thin metal film, exposure, development, etching, and the like (refer to Japanese Patent Laid-open Application No. Hei 7-263841). However, this method requires exposure masks for respective layers, the design and production thereof require a plenty of time and costs. Besides, when alternation, modification or the like of an electronic circuit substrate becomes necessary, a great influence is exerted upon the time of delivery or costs of the electronic circuit substrate.
Because of these disadvantages, a method of forming an electronic circuit substrate by printing using electrophotography is proposed instead of the above method. In this method, an underlying layer for electroless plating having an arbitrary pattern is first prepared by using electrophotography with a charged particle containing fine metal particles in the resin. A plating layer is formed on the underlying layer by electroless plating, and an insulating layer is formed by electrophotography using charged particles made of resin only, so that the electronic circuit substrate is formed.
Note that since the above-described insulating layer requires sufficient electric insulation, it is necessary for it to have a thickness of 20 μm or more. Here, the thickness of the insulating layer formed by printing charged particles in one printing depends on the average particle size of the charged particles. Accordingly, it is conceivable to use charged particles having a large average particle size capable of obtaining a thickness of 20 μm or more in one printing to form an insulating film. However, there are a couple of disadvantages to form an insulating layer by using such large charged particles. One is the generation of a void in the insulating layer. Another is that in the case of using a large charged particle, a pattern cannot be formed because the resolution of a pattern largely depends on the particle size.